Pneumatic springs, commonly referred to as airsprings, have been used with motor vehicles for a number of years to provide cushioning between movable parts of the vehicle primarily to absorb shock loads impressed on the vehicle axle by the wheels striking an object in the road or entering into a depression. These airsprings usually consist of a flexible rubber sleeve or bellows containing a supply of compressed air and having one or more pistons located within the flexible resilient sleeve to cause compression and expansion of the air as the vehicle experiences the road shock. The pistons cause compression and expansion of the fluid within the spring sleeve with the sleeve being of a flexible material permitting the pistons to move axial with respect to each other as the sleeve moves from an extended to a retracted or compressed condition. The flexible sleeves are bellow-shaped or have rolled ends to permit the sleeve to move axially between the jounced or collapsed position in a rebound or expended position without damaging the flexible sleeve in which the pistons are located.
However, should the vehicle wheel experience a severe shock the airspring could extend an excessive amount rupturing the air sleeve requiring replacement and repair of the airspring. To prevent such over extension of the sleeve external restraints are used on many airsprings. These external restraints require separate metal attachments on the vehicle and airspring to limit the extension of the sleeve. Although these external restraints have generally proved effective, they increase the cost of the airspring installation and increase maintenance and repair thereon. Furthermore, these metal parts due to their location on the underside of the vehicle, are subject to the usual corrosion and rust due to the harsh environment to which they are exposed.
No known airspring is being used today which utilizes an internal restraint formed of a flexible non metallic strap material.
U.S. Pat. No. 1,636,386 shows a cushion rebound check strap which extends between an axle of a vehicle and another part thereof to limit the movement of the axle in combination with a leaf spring.
U.S. Pat. No. 2,877,010 shows the mounting of a cable within an elastomer tubular pneumatic member, one end of the cable being fixed to an end member and the other cable end being attached to the valve at the other end of the flexible sleeve to permit the introduction of additional air if the sleeve becomes elongated when overloaded.
U.S. Pat. No. 3,001,610 discloses an oil damper having a chain inside of an auxillary piston to limit the lift thereof.
U.S. Pat. No. 3,664,653 shows a shock absorber consisting of a plurality of pneumatic tires connected together by an internal cable.
U.S. Pat. No. 4,029,305 shows the use of external metal cables in combination with airsprings.
Internal metal cables or other similar internal restraints present a problem if mounted within an airspring since the cable is subject to rust and corrosion and ultimate breakage. Also the metal will rub against the inside of the flexible sleeve possibly resulting in a leak developing in the sleeve wall. Also, the metal will not provide any elongation or stretch to assist in absorbing a load when placed thereon which is desirable to avoid a sudden shock to the vehicle and airspring.
Thus the need has existed for an improved airspring having an internal restraint formed of a nonmetallic member completely eliminating the need for any external restraint means.